When a player holds down the spacebar to jump (or the jump button on a controller), the player's arms and legs to not move properly. This visual, error only appears for self on the client, but it cannot be seen when viewing other players. Other players also do not see this bug happening to you on their screen.

https://youtu.be/Tbr0kUou4WM

In the video, I hold down the spacebar. Notice how my legs and arms appear "stiff". In the 2nd half of the video, I only press the spacebar when I land back on the floor. Notice how my legs and arms flail like they should. This is not an issue on the java edition (java parity, but also just a bug nonetheless).

-This bug also breaks some custom player animations that rely on query.is_jumping as well.
-It has been in the game since the very early days of bedrock edition.